1. Field of the Invention
The present invention relates to an impact absorbing member for vehicle. In particular, it relates to the impact absorbing member which can be suitably fixedly welded to an attaching plate even when thickness of a main body thereof is thin, and which is light-weight and low-price.
2. Description of Related Art
An impact absorbing member for vehicle having a hollow cylindrical shape and being disposed between a side member and a bumper beam of a vehicle has been widely known (refer to Japanese Application Laid-open No. 10-244955, and Japanese Patent Application Laid-open No. 2002-104107). It crushes, receiving a compressive load, axially into a bellows shape to absorb an impact energy.
FIG. 6 is a set of views explaining one example of such the impact absorbing member for vehicle. FIG. 6A is a schematic plan view in which a front bumper beam 10 and members therearound of the vehicle are viewed from an upper part. At front ends of the right and left side members 12R, 12L, crush boxes 14R, 14L are disposed as the impact absorbing member, and the bumper beam 10 is, at right and left ends thereof, attached to the side members 12R, 12L via the crush boxes 14R, 14L.
As shown in FIG. 6B which is a sectional view taken along a line 6B-6B in FIG. 6A, that is the sectional view in the vicinity of the right attaching portion, the crush box 14R includes a main body 20 and a pair of attaching plates 22, 24 welded thereto. In detail, the main body 20 has a hollow cylindrical shape such as an octagonal sectional shape. Each of the attaching plates 22, 24 is fixedly welded to each of axial ends of the main body 20 integral therewith. The crush box 14R is, at both axial ends thereof, fixed to the side member 12R and the bumper beam 10 via the attaching plates 22, 24 with bolts (not shown).
When the crush boxes 14R and 14L receive a compressive load F by an impact applied from a front part of the vehicle, as shown in FIG. 6C, the main body 20 crushes or deforms axially into the bellows shape. Upon deformation, the main body 20 absorbs an impact energy to thereby buffer the impact applied to structural members of the vehicle such as the side member 12R. Here, the crush or deformation into the bellows shape is a phenomenon that the main body 20 is subjected to a buckling at plural points (L-shape minute folds shown in FIG. 6C). Normally, the buckling begins from the axial end of the crush box 14R which comes close to the bumper beam 16, that is a load inputting side thereof, and progresses toward a vehicle body as lapse of time.
Incidentally, the bumper beam 10 is right-and-left symmetrical, and a left attaching portion is constructed in the same manner as the right attaching portion. Also, the bumper beam 10 functions as a reinforcement and an attaching member for the bumper, and to the bumper beam 10 a bumper main body 16 made of synthetic resin and the like is attached integrally.
FIGS. 7A to 7C are views for explaining some modes of a fixedly welded portion between the above main body 20 and one of the attaching plates 22, 24 (FIG. 7 shows the attaching plate 22). In each of FIG. 7A, FIG. 7B and FIG. 7C, an upper view is a perspective view, and a lower view is a sectional view of the fixedly welded portion.
Among them, FIG. 7A shows a case where an axial end of the main body 20 is butted to the attaching plate 22, and a L-shaped bracket 30 is spot-welded to both the main body 20 and the attaching plate 22 to join them each other. FIG. 7B shows a case where an axial end of the main body 20 is bent outwardly in a right angle to form a flange 32 integrally to be fixed to the attaching plate 22 by a spot-welding. FIG. 7C shows a case where an axial end of the main body 20 is butted to the attaching plate 22 in a right angle to be fixed by an arc-welding to the attaching plate 22 integrally.
However, the above case of FIG. 7A requires to prepare the bracket 30 separately and to weld it to the attaching plate 22. As a result, the number of parts increases to cause high-price and heavy-weight. In the case of FIG. 7B, upon application of the compressive load, bending of the flange 32 results in bending of the main body 20 to deteriorate the impact absorbing ability thereof.
On the other hand, in the case of FIG. 7C where the arc-welding is performed with the axial end of the main body 20 being butted to the attaching plate 22, unnecessity of the bracket and the like enables the main body 20 to be constructed in light -weight and low-price, and to exhibit a desired impact energy absorbing ability stably. However, when thickness of the main body 20 is thin, following drawbacks may be caused. That is, the main body 20 of thin thickness may be melted to form a hole thereon, or may be thinned to lower the strength thereof, upon the welding. To avoid such drawback, the main body 20 is required to have the thickness of about 1.4 mm or more.
For satisfying the above requirement, it is conceivable to thin the main body 20, with maintaining the desired impact energy absorbing ability by contriving a shape thereof and the like. Also conceivable is thinning the main body 20 for purpose of absorbing the impact energy by a small load. The small load is applied for example by the impact in a low vehicle speed of about 15 km/h or less, and the main body 20 deforms to decrease a damage of the vehicle. However, the main body 20 is fixedly welded to the attaching member 22 by the arc-welding with the axial end thereof being butted to the attaching member 22, similar to the above-mentioned case, so that there was a problem that the thickness of the main body 20 can be hardly thinned below 1.4 mm.
The present invention is made in view of the above-mentioned circumstances. It is therefore an object of the present invention to provide an impact absorbing member for vehicle, which can realize a desired impact energy absorbing ability, and which is light-weight and low-price, by fixedly arc-welding the main body to the attaching plate suitably even when thickness thereof is thinner than 1.4 mm.